An engine generator as an operating machine driven by an engine is provided with an operation board or an operation box. The operation box has therein a device (AVR) for automatically controlling output voltage generated by the engine generator, an electric wire, and the like, and produces heat when current flows. The heat increases temperature in the operation box and exerts an adverse influence on electronic parts. Consequently, a measure to avoid temperature rise is taken.
For example, Japanese Utility Model Application Laid-Open (JP-U) No. 63-125129 discloses an engine generator having a control box disposed on the generator. A port communicated with the control box is provided in a rear-part peripheral wall of the generator, and the control box has an outside air intake port. In the engine generator, the inside of the control box is cooled by making outside air taken from the outside air intake port, pass through the communication port, and circulated in the casing of the generator by suction force generated by a ventilation fan.
Japanese Utility Model Application Laid-Open (JP-U) No. 05-58826 discloses a structure, in a soundproof case in which cooling air from a cooling fan is sucked in a fan case of an engine, circulated around the engine, and discharged and, an operation board is positioned on the front side of an upper half of the fan case.